02-10-2012, 02:02 PM
3D Modeling From 2D Images
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ABSTRACT
The transition from the set of images into 3D model. Direct
method of creating 3D model using 3D software will be
described. Creating photorealistic 3D models from a set of
photographs is challenging problem in computer vision
because the technology is still in its development stage while
the demands for 3D technology and for new methods of 3D
reconstruction are increasing rapidly. The traditional
approach of computer graphics has been to create a
geometric model in 3D and try to reproduce it onto a twodimensional
image with rendering. A method that is
presented in this article, unlike traditional approach, explains
ways to create photorealistic 3D models from 2D images. It is
mostly focused on detecting, grouping, and extracting
features (edges, faces, etc.) present in a given picture and then
trying to interpret them as three-dimensional clues. The
results obtained can be displayed using new technologies such
as 3D monitor or printed on the 3D printer. In operational
part of this article, it will be specifically explained how to
create photorealistic human face from the set of images with
two different methods automatic and direct. We will offer a
solution to the problems that occur in the reconstruction of
3D models from photos, such as variations in geometric scale
and a mix of textured, uniformly colored, and reflective
surfaces.
INTRODUCTION
In the last ten years, a significant progress occurred in the
area of 3D graphics. Many studies have been conducted in
the field of 3D modeling, and a variety of methods that
allow us to reconstruct 2D images into 3D were created.
Today, 3D graphics industry creates models that can no
longer be distinguished from a person in the real world or
on photograph. This way of modeling is also the goal of
this work; to explore options to create a photorealistic 3D
model shaped from the 2D images. This article has listed
and briefly described methods of converting 2D images
into 3D models. Automatic method of creating and
modeling "the head" in Facegen and Faceshop programs
and manual processing with 3D modeling programs using
photos or film (2D) test with "supek" illustration is
described in detail. These methods were chosen because
they create a solid 3D model. There are other methods such
as stereoscopy, which show us a 3D scene but its depth is
illusive. Such methods are good if the ultimate goal is onscreen
visualization only, but if you need to create a solid
3D model for 3D printing, it is necessary to use automatic
or manual modeling.
MODEL RECORDING
This section will describe in detail, the proper way of
recording the model with the camera, and automatic
method of making the 3D model through the obtained
recordings. When it comes to facial reconstruction from
series of photographs, there will almost always be some
errors that occur due to the moving of the person. One of
possible solutions is to simultaneously record with multiple
cameras from different angles. Three cameras are
distributed in a circle around the subject, angle set to 90°
(profiles and in front of the face) simultaneously recording
the subject. In such a way we obtain images in which the
error of changing the position of the object will be
minimal. But in most cases, while recording, there is only
one camera, which circles around the subject.
AUTOMATIC FACE MODELING METHOD
Method which automatically creates 3D face model can be
obtained with very good results if we use HDR and tonemapping
methods of image processing. This method is
good because of speed in creating the solid 3D model, but
not good if we want a photorealistic model, since it
contains errors such as: the structure of the skin does not
exist, and there is only a basic face shape. If the image
contains a variety of facial expressions, or lack details
because of shadowed parts, the program will take the
middle, and will lack the face characterization. The
positive side is that this method can be used to create the
base model (zero model) for further processing.
USE OF HDR METHOD
High Dynamic Range Imaging method and Tone-mapping
are largely described in reference [1]. To obtain high
quality illumination on image, and to highlight its details
hidden in the shade we can use the HDR method. It
contains three shots filmed from the same position and
embedded in one image. The difference between these
shots is the length of exposure. The first shot must be over
exposed, second under exposed, and third under optimal
exposure. By combining these three shots we obtain the
optimal tone values in all areas, with more detail in bright
and dark areas. In such a way we increase the quantities of
small details, and face acquires specific character. There
are two methods of creating HDR images. The real HDR is
filmed with three shots as described, while for creating
false HDR it requires only one.
Image orientation
Image orientation involves setting up different profiles
depending on the head rotation. If the frontal image is used
solely, there will be no texture on the profiles. Blank fields
will appear or will be spread on faces, depending on their
number and position. There is still no software that would
automatically resolve this problem. Different head
positions have to contain the exactly same position in
reality. The three images here are set to face three positions
as follows: frontal shot and the two profiles. The pictures
are marked by key points as described. The program
automatically applies the selected texture points. We get a
good coverage of the face with texture, observed from
different angles. During rotation, mesh model has no
empty areas, and texture settles on mesh surfaces. Like on
Figure 3. Finally, the images that are applied to the model
must be fully equal in all characteristics, except by the
angle of shooting. After obtaining the 3D model, it is
exported as obj.file or 3ds.file, to finish with the direct
method.
RENDERING
The final step of creating a model is rendering. Rendering
is a mathematical process of createing 2D images from 3D
models. In this case, the rendering will be used only to see
the final result of the work. Even though the 3D programs
create their own lighting in 3D space, it doesn’t provide a
realistic view of the model. Many parts remain shaded and
invisible; therefore it is necessary to start the rendering
process. It allows us to view the model as it looks in
reality. It is required to perform rendering on each side of
the model, and that can be achieved in two ways. First way
is to turn the view of the model and render each image
separately. It provides us with an overview of the model,
and the process is much faster and easier than creating
animation.
Other way is to create a short animation of rotating object.
This is complicated because, not only the view turns but
the model as well. The bright side is that these animations
can provide better sight of the object. To get an overview
of how the model looks like in reality, it is necessary to set
the correct lighting. Light reflection from the object
depends on its outer surface as well as the type of light
objects set in 3D space. This process is unavoidable,
especially if the ultimate purpose of modeling (except
screen viewing), is 3D printing process. Considering that
the 3D printing is an expensive process, errors on the
model are unacceptable, so rendering is the only way to
find out what will the model look like in reality. It is
recommended to execute the process of Photorealistic
Rendering if the software grants it. Photorealistic
Rendering is a blend of art and science which creates
images and scenes that completely mimic the real world.
This can be achieved with a computer algorithm that
converts a 3D model to 2D image, while taking the value
of realistic illumination. There are several software
packages that can be used to achieve this goal. One of the
tools that came on the market in order to create these
highly sophisticated images is Renderman (Pixar,
http://www.pixar.com). Renderman is developed and
released publicly by Pixar in the 1980's, and it became a
standard for 3D photorealistic rendering and animation.
CONCLUSION
The ultimate goal of current research in the field of
modeling is to find a system that creates realistic animation
in real-time, is fully automated and easily adapts to the
individual’s face. Such a program will probably be
available in the near future, as for now, the modeling based
on manual and automatic design (which, as seen in testing
described in this article), doesn’t provide satisfying results.
Ergo, combined procedure was implemented with
automatic and direct methods of modeling. Finally, such a
procedure has many advantages especially when used with
HDR and Tone-mapping methods of processing 2D shots.
Some of them are: less time and effort is required to obtain
realistic models (because the process is semiautomatic),
it’s easier to create, it provides a greater chance of creating
realistic models, and finally, getting the texture-mapping
arranged by UV coordinates is automatic. It is necessary to
record from different angles, and to acquire shots of high
resolution and normal illumination, if not the entire process
of creating photorealistic model is almost impossible.
Realistic look of the model depends solely on the skills and
experience of the designer. However, there are many ways
to improve the existing method, and to generate space for
further research.